3,366,622 United States Patent Office Patented Jan. 30, 1968 2 3,366,622 phenyl) and aralkyl having from 1-5 carbon atoms in OX DATION OF HYDRAZOAM DES TO the alkyl chain (for example naphthyl ethyl, but prefer AZOFORMAMDES ably benzyl) groups. John Minton Chalinor and Neil William Woodrow Acording to a preferred embodiment of the invention Porter, Loughborough, England, assignors to Whif 5 R, R, R8 and R4 are each hydrogen. fen & Sons Limited, Loughborough, England The bromine or bromide may be present in amounts No Drawing. Filed July 27, 1965, Ser. No. 475,244 varying over a wide range, but essentially only requires Claims priority, application Great Britain, Aug. 11, 1964, to be present in catalytic amounts. The amount of bro 32,761/64; Oct. 22, 1964, 43,045/64 mine or bromide suitably comprises from 0.1 to 20% 10 Claims. (Cl. 260-192) O by Weight based on the hydrazoamide starting material, and preferably comprises 1 to 10% by weight on the hydrazoamide starting material. Bromides which may be ABSTRACT OF THE DISCLOSURE mentioned include alkali metal bromides, such as for A process for the oxidation of an hydrazoamide, such example sodium bromide and potassium bromide, alkaline as hydrazoformamide to azoformamide, in high yield 5 earth metal bromides, such as for example calcium bro without contamination by the starting material, which mide and barium bromide; other metal bromides such process comprises oxidizing the hydrazoamide with a as for example ferric bromide, chromic bromide, copper water-soluble chlorate in an aqueous acidic medium hav bromide, strontium bromide, cobaltic bromide and zinc ing a pH in the range of 2.0 to 0.5 in the presence of bromide; hydrobromic acid; and halogenobromides such a catalytic amount of bromide or bromine. 20 as bromine monochloride. Similarly the bromide may be an organic bromide such as a quaternary ammonium was airwan bromide such as tetramethylammonium bromide or tetra The present invention concerns an improved method ethylammonium bromide. for the oxidation of hydrazoamides. The concentration of bromide or bromine in the total The oxidation of hydrazoamides to azoamides presents 25 reaction liquor is suitably in excess of 0.01% weight/ various problems; it is generally desired to obtain the volume, and is preferably in the range 0.5 to 10% weight/ azoamide product free from hydrazoamide, and although Volume. The weight/volume ratio is calculated as grams/ it is possible to separate hydrazoamide from azoamide, cubic centimetre. this is not practicable commercially. However with many . By the term pH as used in the specification and claims oxidation methods, if the oxidation is continued to com 30 is meant pH calculated according to the formula plete oxidation, the product azoamide is also oxidised with loss of yield. Furthermore several oxidation methods. pH= -log10 (hydrogen ion concentration) for example with dichromates, involve effluent disposal wherein monobasic acids (such as hydrochloric acid) are problems. assumed to be fully ionised and polybasic acids (such It has now surprisingly been found that hydrazoamides as Sulphuric acid) are assumed to have the first hydrogen may be readily oxidised in high yields to the correspond atom fully ionised and the other hydrogen atom(s) non ing azoamides by oxidation with a water-soluble chlorate ionised. providing that the oxidation is carried out in the presence It is preferred to carry out the process in the presence of high concentrations of hydrogen ion and in the presence of hydrochloric acid or sulphuric acid or a mixture there of catalytic amounts of bromine or a bromide; by this 40 of; other acids such as phosphoric acid may be used if process it is possible to obtain high yields of the azo fired, but oxidising acids such as nitric acid are unsuita amides free from the hydrazoamide starting material. This C. process involves minimal effluent problems. During the process, there is an increasing dilution as Accordingly the present invention is for the oxidation Some water is formed in the oxidation process, and in of hydrazoamides of the formula: 45 many cases the chlorate is added as an aqueous solution. Consequently the acidity at the end of the oxidation is more significant than the acidity at the beginning of the reaction. It is preferred to carry out the process with the pH in the range -0.5 to -1.0 throughout the reac where R, R2, R3 and R4 are selected from the groups 50 tion. - comprising hydrogen, alkyl, cycloalkyl, aryl and aralkyl The water soluble chlorate may be for example an groups, substituted or unsubstituted, to the corresponding alkali metal chlorate such as potassium chlorate or sodium azoamide, by treatment with a water-soluble chlorate chlorate; an alkaline earth metal chlorate such as calcium in an acidic medium having a pH as herein defined in chlorate; and other metal chlorates such as magnesium the range -2.0 to -0.5 in the presence of bromine or 55 chlorate, zinc chlorate, lead chlorate or silver chlorate. a bromide. The pH is preferably in the range -1.0 However it is essential to use a metal which forms a to 0.5. Soluble Salt of the acid employed, as otherwise the product In the above formula R, R2, R3 and R4 may each be is contaminated with the insoluble metal salt. It is pre the same or different. Where R, R2, R8 and R4 are alkyl, ferred to use an alkali metal chlorate, specifically sodium cycloalkyl, aryl or aralkyl groups, these may be substituted 60 chlorate, which is also the cheapest available chlorate. or unsubstituted. Where substituted, the substituent groups The chlorate may be added to the reaction mixture in may comprise for example chloro or nitro groups. How the form of a solution in water or may be added as a ever it is preferred that these groups should be unsub solid, whichever is found most convenient. stituted. The amount of chlorate used in the oxidation must According to one embodiment of the invention, in the 65 be at least the stoichiometric equivalent amount if com formula above, R, R2, R3 and R4 are the same or dif plete oxidation is to be obtained. ferent and are selected from hydrogen, alkyl (for example The present invention is particularly concerned with alkyl with from 1-12 carbon atoms, such as n-propyl, the oxidation of hydrazoformamide to azoformamide, isobutyl, octyl and dodecyl, but preferably methyl and which is used widely as a blowing agent. For this pur ethyl), cycloalkyl (such as cyclopentyl and cyclohexyl), 70 pose the azoformamide requires to be completely free aryl (such as ethylphenyl and naphthyl, but preferably from hydrazoformamide, and it is a special feature of the 3,366,622 3. 4. invention that the present process provides a simple Example 5 method for the oxidation of hydrazoformamide to azo The process of Example 3 was repeated exactly as de formamide in high yields giving a product free from hy scribed, but carried out at a temperature of 50-55 C. drazoformamide. In order to obtain this result, an excess 94 grams of azoformamide were obtained. of chlorate over the stoichiometric amount is required; Example 6 the excess may be up to 100% or more over this amount, although such large excesses are not strictly required for The process of Example 3 was repeated exactly as de the process. Satisfactory results are obtained with up to scribed but carried out at a temperature of 60-65 C. 91 15% excess over the stoichiometric amount; it is pre grams of azoformamide were obtained, containing no de ferred to use a 5-10% excess over this amount. tectable amount of hydrazoformamide. The present invention provides a method of obtaining O Example 7 very high yields of azoformamide free from hydrazoform 32 grams of Solid sodium chlorate was added in por amide. In other oxidation processes, complete oxidation tions over 45 minutes to a stirred suspension containing may only be obtainable in reduced yields, as the condi 100 grams of hydrazoformamide, 61 millilitres of 36% tions to obtain complete oxidation lead to decomposition 5 hydrochloric acid in 81 millilitres of water, and 0.5 gram of the azoformamide product. of bromine. The reaction temperature was maintained at The oxidation may be carried out at elevated tempera 40-45°; the pH at the start of the process was -0.70 and tures desirably in excess of 25 C. Temperatures in ex at the finish of the process was -0.65. The azoformamide cess of 75 C. may be used, if desired, but less satisfactory product (96 grams) was filtered, washed and dried. This results are obtained generally. It is preferred to carry out 20 was found to contain no detectable amount of hydrazo the reaction at temperatures in the range about 25-50 C. formamide. The oxidation may be carried out under atmospheric Example 8 pressure, reduced pressure or elevated pressure. 32 grams solid sodium chlorate was added in portions The following examples, in which percentages are by over 45 minutes to a stirred suspension containing 100 weight, illustrate the process of the present invention. 25 grams hydrazoformamide, 60 grams concentrated sul Example 1 phuric acid in 94 millilitres of water and 1.0 gram of cobalt bromide. The reaction temperature was maintained A solution containing 30.9 grams of sodium chlorate at 40-45°; the pH at the start of the process was -0.78 in 50 millilitres of water was added over 37.5 minutes and at the finish of the process was -0.74. The azoform to a stirred suspension containing 100 grams of hydrazo 30 amide product (97 grams) was filtered, washed and dried formannide, 110 millilitres of 36% hydrochloric acid in and was found to contain no detectable amount of hy 70 millilitres of water and 3.75 grams of sodium bromide. drazoformamide. The reaction temperature was maintained at 37.5 C.; Example 9 the pH at the start of the process was -0.85 and at the The process of Example 3 was repeated exactly as de finish of the process was -0.75. 96.5 grams of an or 35 scribed replacing the hydrazoformannide by methylhy ange azoformamide were obtained, which was washed, drazoformamide. 92 parts of monomethylazoformamide filtered and dried. The azoformamide contained no de were obtained. tectable quantity of hydrazoformamide. Example 10 Example 2 40 The process of Example 3 was repeated exactly as de A solution containing 35 grams of calcium chlorate in scribed replacing the hydrazoformamide by N-methyl-N- 50 millilitres of water was added over 40 minutes to a phenylhydrazoformamide. 82 parts of N - methyl - N stirred suspension containing 100 grams of hydrazoform phenylazoformamide were obtained. amide, 113 millilitres of 36% hydrochloric acid in 72 Example 11 millilitres of water and 4.5 grams of potassium bromide. The reaction temperature was maintained at 40° C.; the 45 The process of Example 3 was repeated exactly as de pH at the start of the process was -0.85 and at the finish scribed replacing the hydrazoformamide by N-ethyl-N- of the process was -0.75. 96 grams of azoformamide phenyl-N'-methylhydrazoformamide. 96 parts of N-ethyl were obtained, which was washed, filtered and dried. The N-phenyl-N'-methyldrazoformamide were obtained. aZoformamide contained no detectable quantity of hydra 50 Example 12 Zoformamide. The process of Example 3 was repeated exactly as de Example 3 scribed replacing the hydrazoformamide by N,N,N',N'- A solution containing 32 grams sodium chlorate in 45 tetrabenzylhydrazoformamide. 92 parts of N,N,N',N'- millilitres of aqueous solution was added over 45 min tetrabenzylazoformamide were obtained. utes to a stirred suspension containing 100 grams of hy 55 drazoformamide, 61 millilitres of 36% hydrochloric acid Example 13 in 59 millilitres of water, and 0.5 gram sodium bromide. The process of Example 3 was repeated exactly as de The reaction temperature was maintained at 40-45; scribed replacing the hydrazoformamide by N-methyl-N- the pH at the start of the process was -0.77 and at the phenyl - N' - benzyl- N' - (7 - ethylnaphthyl) hydrazo finish of the process was -0.63. The azoformamide prod 60 formamide. 88 parts of N-methyl-N-phenyl-N'-benzyl-N'- uct (96 grams) was filtered, washed and dried, and con (7-ethylnaphthyl) azoformamide were obtained. tained no detectable quantity of hydrazoformamide. Example 14 Example 4 The process of Example 3 was repeated exactly as de A solution containing 33 grams sodium chlorate in 80 scribed replacing the hydrazoformamide by N,N-di millilitres of aqueous solution was added over 45 min methyl- N'-cyclohexyl- N'-n - dodecyl -hydrazoforma utes to a stirred suspension containing 100 grams of hy. mide. 85 parts of N,N-dimethyl-N'-cyclohexyl-N'-n- drazoformamide, 71.5 grams of concentrated sulphuric dodecyl-azoformamide were obtained. acid in 94 millilitres of water and 0.5 gram of sodium We claim: bromide. The reaction temperature was maintained at 70 1. A process for the oxidation of hydrazoamides of the 40-45; the pH at the start of the process was -1.04 formula: and at the finish of the process was -0.83. The azoform amide product (97 grams) was filtered, washed and dried, and was found to contain no detectable quantity of hydra Zoformamide. 75 3,366,622 5 6 where R, R2, R3, and R4 are selected from the group con 9. A process as claimed in claim 1 wherein the bromide sisting of hydrogen, alkyl, cycloalkyl, aryl and aralkyl is selected from the group consisting of halogenobromides, groups, and the chloro and nitro-substituents thereof to hydrobromic acid, alkali metal bromides, alkaline earth the corresponding azoamide which comprises treating the metal bromides, ferric bromide, chromic bromide, copper hydrazoamide with a water soluble chlorate in an aqueous bromide, strontium bromide, cobaltic bromide, zinc acidic medium having a pH in the range of -2.0 to -0.5 bromide and quaternary ammonium bromide. in the presence of a compound selected from the group 10. A process for the production of azoformamide consisting of bromine and bromides. which comprises oxidising hydrabroamide by treatment 2. A process as claimed in claim 1 wherein R, R2, R8 with sodium chlorate in an aqueous acidic medium con and R4 are each hydrogen. taining an acid selected from the group consisting of hy 3. A process as claimed in claim wherein the chlorate 0. drochloric acid and sulphuric acid, at a pH below 0, in is sodium chlorate. the presence of a compound selected from the group con 4. A process as claimed in claim wherein the bromine sisting of bromine and bromides in amount comprising or bromide is present in amount comprising 0.1 to 20% 0.1 to 20% by weight of the hydrazoformamide starting by weight of the hydrazoamide starting material. material and in a concentration in excess of 0.01% 5. A process as claimed in claim wherein the concen 5 weight/volume. tration of the bromine compound in the reaction medium is in excess of 0.01% weight/volume. References Cited 6. A process as claimed in claim 1 wherein the oxida UNITED STATES PATENTS tion is carried out at a temperature in the range 25 to 3, 190,873 6/1965 Porter ------260-192 50° C. 20 7. A process as claimed in claim 1 wherein the pH of FOREIGN PATENTS the reaction medium is in the range of -0.5 to -1.0 throughout the reaction. 959,761 6/1964 Great Britain. 8. A process as claimed in claim 1 wherein the chlorate 1,344,799 10/1963 France. is used in amount comprising 5-10% excess over the 25 22,567 10/1963 Japan. Stoichiometric amount. FLOYD D. HIGEL, Primary Examiner.